1. Field
This invention pertains generally to hematology and specifically to a novel form of hematological control. It provides both a stabilized animal platelet control and a method for checking the threshold calibration of electronic particle counters.
2. State of the Art
The use of electronic particle counters in hematology is well known. U.S. Pat. No. 2,656,508 discloses a basic apparatus utilizing the Coulter principle for this purpose. U.S. Pat. No. 3,757,213 contains a description of several such devices which incorporate threshold circuitry. Threshold circuitry excludes random amplitude signals caused by noise and background debris or inconsequential particles in the suspension. It may also be used to limit the size range of particles counted. Adjustable threshold circuits with dials marked off in mathematically related dial settings are in common use. The mathematical relationship may, but need not necessarily, be linear. Coulter Electronics, Inc. of Hileah, Fla. supplies a number of publications which describe the operation of various models of electronic particle counters pertinent to this disclosure. For example, CMS catalogue No. 360-529 is an instruction manual for the Coulter Model ZBI. Coulter Electronics, Inc. also publishes an operator's reference manual for its Model S Plus (Coulter Part No. 6601221, copyrighted 1977, 1978). The disclosures of all of the foregoing patents and operators' manuals are incorporated herein by reference.
Although this disclosure will be directed primarily to embodiments involving the use of electronic particle counters of the Coulter type, it should be understood that the platelet controls herein disclosed, and their methods of use described herein, find wide application with particle counters generally. Accordingly, the term "electronic particle counter", as used herein, should be understood to include, in addition to Coulter Counters, any other type of particle counter which discriminates between particles of various sizes by the use of electronic discriminator circuits ("thresholds") which respond electronically to signals indicative of particle size, mass or other parameters related to particle volume; including those employing light scatter.
Calibration check techniques for red blood cell (erythrocytes) counts and white blood cell (leukocytes) counts are well developed. The techniques generally involve counting known populations of particles suspended in a liquid vehicle in a "control" preparation. The control preparation is usually diluted substantially (e.g., 1:3000) with a diluent prior to counting. Heretofore, however, no satisfactory platelet control for use with manual, semi-automated and automated counters has been available. Moreover, there has not heretofore evolved a reliable method and control preparation for determining the threshold factor to be applied to the control dials of threshold circuits. That is, although counts are routinely taken and reported between threshold dial values selected to fix both a lower particle size and an upper particle size for the count, the electronic volume sizes of the smallest and largest particles actually being counted are not fixed parameters on adjustable threshold particle counters. There is thus a need in the art for a reliable check of threshold calibration for electronic particle counters of the type typified by the semi-automated Coulter Counters. Operators could then identify and document the volume ranges between which platelets are to be routinely counted. There is further a need in the art for a reliable method for demonstrating instrument stability over a prolonged period of use.